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TPS61165: Have this driver powering five white LEDs in parallel on a NHD TFT display, PWM does not seem to work.

TIM CRIST
Prodigy 10 points
Part Number: TPS61165
Other Parts Discussed in Thread: TPS61166

Tool/software:

NHD suggested this part and schematic.   My TFT has 5 white LEDs in parallel.  The driver Vin is 5V and control is from a 3.3V GPIO output.

PWM frequency is 25Khz.

It just stays on all the time and does not respond to PWM from 100% to 0%.  What am I doing wrong.  (SCH attached).

  • 0
    TI__Mastermind 21041 points

    Hi Tim，

    This schematic looks good to me.

    Could you check your CTRL, SW and LEDA waveforms?

    Thanks,

    Colin

  • 0
    Prodigy 10 points

    Colin,

    Seems the issue is the NHD TFT display we are using has the backlight LEDs in parallel.  Vf for those LEDs is 2.8 to 3.4V.  Consequently, the 5V supply on the TPS61165 never begins to regulate, instead, Rsense at 33 ohms limits the current to around (5-3)/33 = 60mA or so.   

    Next question, would dropping 5V to 3V and using the TPS61166 here work to regulate to 100mA for LEDs as well as allow it to turn off at 0 percent DC on a PWM?

    Thanks,

    Tim

  • 0 in reply to TIM CRIST
    TI__Mastermind 21041 points

    Hi Tim,

    The current depends on below equation:

    .

    Please make sure the input power is stable. 

    Second question; TPS61166 can support 3V working.

    Thanks,

    Colin